bio207 exam4

Describe 2-3 physical barriers of the body to prevent microbial infections.

Skin with tightly packed keratinocytes, mucous membranes with cilia, and the mucociliary escalator in the lungs physically block and remove microbes.

keratinocytes

main cells of epidermis (outer skin layer) forming protective barrier against pathogens, produce keratin

mucous membrane with cilia location/ purpose

line respiratory track, hair like projections that move microbes up and out of the airways

mucociliary escalator in the lungs

use sticky mucous to trap debris in lungs, cilia move them upwards and out. prevent infection and inflammation

Describe 2-3 chemical barriers of the body to prevent microbial infections.

Stomach acid, lysozyme in saliva and mucus, and defensins that form pores in microbes act as chemical defenses.

lysozyme

enzyme in bodily fluids (tears, saliva, milk) that breaks down bacterial cell walls

defensins

form transmembrane pores in microbes= cellular contents leak out and cell lysis

What is the role of lymphoid organs in the human immune system?

Lymphoid organs are where lymphocytes mature and become activated to recognize specific antigens.

How do natural killer cells fight infection? (Use MHC I, perforin, apoptosis)

Natural killer cells recognize cells lacking MHC Class I (some cancers repress these surface proteins and become targets for NK cells) and release perforin to form pores that allow granzymes to enter and trigger apoptosis.

What are MAMPs and what is their role in ? immunity?

MAMPs are conserved microbial molecules that are recognized by PRRs to activate the innate immune response.

innate immunity

body's first, non-specific defense (skin, fever, inflammation) present from birth, acting immediately but generally against all germs

specific/ adaptive immunity

learned, targeted response involving T & B cells that develops over time, creating memory for faster, powerful attacks against specific pathogens later on (post vaccines or infection)

You get a splinter in your hand—describe the inflammatory response using the given terms.

Macrophages release cytokines that signal neutrophils to leave blood vessels by extravasation, move to the wound, and perform phagocytosis to destroy microbes.

Describe the roles of macrophages, phagosomes, and lysosomes in phagocytosis.

Macrophages engulf microbes into phagosomes, which fuse with lysosomes to form phagolysosomes that destroy microbes using enzymes and oxygen radicals.

What 2 killing pathways do phagolysosomes use?

Oxygen-independent pathways using lysozyme, lactoferrin, and defensins, and oxygen-dependent pathways using reactive oxygen species during the oxidative burst.

What can lead to chronic inflammation?

Persistent pathogens, nonliving irritants like splinters or asbestos, and autoimmune diseases can cause chronic inflammation with permanent tissue damage.

Is complement more effective against Gram(+) or Gram(-) bacteria and why?

Complement is more effective against Gram(-) bacteria because their thinner cell wall allows the membrane attack complex to form pores more easily.

What is the benefit of fever?

Fever raises body temperature to slow microbial growth and improve immune cell function. (helper T cells release more cytokines at higher temps)

Innate immunity

The nonspecific immune defense that is present at birth and includes physical barriers, chemical barriers, and immediate cellular responses to pathogens.

Adaptive immunity

The specific immune response that develops after exposure to an antigen and has memory for faster future responses.

Antigen

Any foreign chemical, compound, or structure that triggers an immune response.

Gut-associated lymphoid tissue (GALT)

Immune tissue in the gastrointestinal tract (including tonsils and Peyer's patches) that samples microbes and links innate and adaptive immunity.

Peyers patches

in small intestine, use M cells to transport antigens in gut to immune cells (T and B lymphocytes)

Defensins

Small antimicrobial proteins that insert into microbial membranes and form pores to kill invading cells.

Neutrophil

A white blood cell and phagocyte that exits the bloodstream by extravasation and engulfs pathogens during inflammation.

Lymphocytes

White blood cells (B cells, T cells, and NK cells) involved mainly in adaptive immunity and found mostly in lymphoid organs.

Natural killer (NK) cells

Innate immune cells that kill infected or cancerous cells that lack MHC Class I using perforin and apoptosis.

Major histocompatibility complex (MHC)

Host cell surface molecules that display "self" markers and help immune cells recognize infected cells.

MHC Class I

A type of MHC found on healthy cells; loss of MHC I signals NK cells to destroy the cell.

Microbe-associated molecular patterns (MAMPs)

Conserved microbial structures recognized as foreign by the innate immune system.

Pattern recognition receptors (PRRs)

Host receptors such as Toll-like and NOD-like receptors that detect MAMPs and activate immune responses.

Phagocytosis

The process by which immune cells engulf and digest microbes.

Macrophages

Large phagocytic immune cells that engulf microbes, release cytokines, and activate adaptive immunity (presents antigens to helper T cells)

Phagosome

A membrane-bound vesicle that forms around a microbe after it is engulfed by a phagocyte.

Lysosome

An organelle containing digestive enzymes that fuses with the phagosome to destroy microbes.

Complement system

A group of ~20 blood proteins that form pores in microbes, attract leukocytes, and enhance phagocytosis.

Pyrogens

Substances that cause fever by stimulating prostaglandin release and raising body temperature.

Antigen —

Any substance that induces the immune system to produce antibodies, including parts of microbes, chemicals, toxins, or pollen.

Epitope —

The specific molecular part of an antigen that is recognized by an antibody or immune cell receptor.

Antigen-presenting cell (APC) —

A cell (dendritic cell, macrophage, or B cell) that degrades pathogens then attaches antigens to MHC molecules, and presents them to T cells.

MHC Class I — presents to what?

A molecule found on all nucleated cells that presents intracellular antigens to cytotoxic (killer) T cells.

MHC Class II —

specialized: antigen-presenting cells (presents antigens on their surface to T cells) that presents external antigens to helper T cells.

Antibody —

A Y-shaped immunoglobulin protein produced by B cells that specifically binds antigens. (paratop binds to epitope, marking pathogen for destruction)

Immunological specificity —

The ability of antibodies to bind only to the specific epitope that triggered their production.

Primary antibody response —

The first immune response to an antigen, producing IgM first, then IgG, and forming memory B cells.

Secondary antibody response —

A rapid, larger antibody response after re-exposure, dominated by IgG due to memory B cells.

Humoral immunity —

Antibody-based adaptive immunity mediated by B cells and effective against extracellular pathogens.

Cell-mediated immunity —

T-cell-based immunity that destroys infected host cells and targets intracellular pathogens (microbes hide inside host cell) like viruses.

Cytokines —

Signaling molecules that direct immune cell activity and determine whether humoral or cell-mediated immunity is activated.

B cell —

A lymphocyte that produces antibodies during humoral immunity.

T cell —

A lymphocyte involved in cell-mediated immunity that helps activate immune responses or kills infected cells.

Isotypes —

Antibody classes shared by all members of a species, such as IgG, IgM, IgA, IgD, and IgE.

Allotypes —

Antibody variations found among some individuals of the same species due to small amino acid differences.

Idiotypes —

Antibody differences within the same individual that occur in antigen-binding regions and determine antigen specificity.

specific "fingerprint" of a particular antibody's antigen recognition site

Contrast humoral immunity and cell-mediated immunity.

Humoral immunity uses B cells and antibodies to target extracellular pathogens, while cell-mediated immunity uses T cells to destroy infected host cells and intracellular pathogens.

What is the distinction between an antigen and an allergen?

An antigen triggers an immune response, while an allergen is a non-infectious antigen that causes an allergic response.

How does vaccination make use of the adaptive immune response? (live attenuated example)

Vaccination introduces a weakened pathogen that triggers antibody production and memory cell formation without causing disease.

Contrast the primary and secondary antibody responses.

Primary responses are slow, low-level, and dominated by IgM, while secondary responses are rapid, high-level, and dominated by IgG.

How does our body generate so many different antibodies with limited genes?

Antibody diversity is created through DNA rearrangements of antibody gene segments within differentiating B cells.

How do the roles of MHC I and MHC II differ?

MHC I presents intracellular antigens to cytotoxic T cells, while MHC II presents extracellular antigens to helper T cells.

What strategies have pathogens evolved to evade adaptive immunity?

Pathogens reduce MHC I expression, trigger T-cell apoptosis, disrupt cytokine signaling, or rapidly mutate antigens.

(Lactic) Acid fermentation —

A type of fermentation in which bacteria convert sugars into lactic acid, producing the sour taste of foods like yogurt, cheese, pickles, and fermented meats.

Alcoholic fermentation —

A type of fermentation in which yeast convert sugars into ethanol and carbon dioxide, used in bread, wine, and beer production.

Starter culture —

A carefully selected group of microbes intentionally added to food to produce predictable fermentation, flavor, and texture.

Unripened cheese —

Soft cheese that relies only on bacterial fermentation for acidification and coagulation, such as cottage cheese.

• stops fermentation early

Ripened cheese —

Cheese that undergoes additional aging (fermentation) and microbial fermentation after curd formation to develop stronger flavor, such as Swiss or Roquefort.

Intrinsic risk factors —

Internal properties of food that affect spoilage, including water availability, pH, nutrients, biological barriers, and antimicrobial chemicals.

Extrinsic risk factors —

Environmental conditions affecting food spoilage, including storage temperature and atmospheric oxygen.

Food spoilage —

Microbial growth that causes food to become unpalatable through acid production, fat rancidity, protein decomposition, or bitterness.

Food poisoning —

Illness caused by ingestion of microbial toxins already present in food, with symptoms appearing within hours and not prevented by reheating.

Food infection —

Illness caused by ingesting live pathogens that grow inside the body, with symptoms appearing after a day or more.

Adhesin —

A microbial surface structure that allows pathogens to attach to host cells.

(Fimbriae) Pili —

Hair-like bacterial surface structures used for attachment and colonization of host tissue.

Exotoxin —

A toxic protein actively secreted by bacteria that damages host cells.

Endotoxin —

A toxic component of the lipopolysaccharide (LPS) of Gram-negative bacteria that overstimulates the immune system.

Type II secretion system —

A bacterial protein secretion system used to export toxins and enzymes outside the cell.

Type III secretion system —

A needle-like secretion system that injects toxins directly into host cells.

Enterotoxin —

A heat-stable toxin that targets the intestines and causes rapid watery diarrhea without infection.

Prion —

A misfolded infectious protein that causes neurodegenerative disease and contains no DNA or RNA.

Why are bacterial and eukaryotic microbes used differently as direct microbial foods?

Eukaryotic microbes like fungi and algae are used directly as food because they are larger and safer, while bacteria are rarely eaten directly due to toxin production and pathogenic risk.

What are the reasons we ferment food?

Fermentation preserves food, improves digestibility, and enhances flavor and nutritional value.

Contrast lactic acid and ethanolic fermentation in food production.

Lactic acid fermentation produces yogurt, cheese, and pickles using bacteria, while alcoholic fermentation produces bread, beer, and wine using yeast that generate ethanol and CO₂.

What risk factors influence food spoilage?

Intrinsic factors include water content, pH, nutrients, and antimicrobial compounds, while extrinsic factors include temperature and oxygen availability.

Why are some foods more prone to spoilage than others?

Moist, nutrient-rich, neutral-pH foods spoil quickly, while dry, acidic, or salty foods spoil more slowly.

What distinguishes a pathogen from a spoilage organism?

Pathogens possess specific virulence mechanisms that allow host infection, while spoilage organisms only degrade food.

What is the difference between food poisoning and food infection?

Food poisoning results from toxins in food and causes rapid illness, while food infection results from live microbes growing in the body and develops more slowly.

Why is botulism especially dangerous in canned foods?

Clostridium botulinum grows in anaerobic conditions, produces a deadly neurotoxin, and survives poor heating through spore formation.

What is the difference between exotoxins and endotoxins?

Exotoxins are secreted proteins with specific effects, while endotoxins are LPS components of Gram-negative bacteria that trigger massive immune responses.

What makes an enterotoxin different from other toxins?

Enterotoxins specifically target the intestines and cause rapid watery diarrhea without infection.

What are the most common causative agents of diarrheal disease?

The most common are norovirus and rotavirus, followed by Salmonella, E.coli, Campylobacter

Clostridium botulinum —

Soil bacterium in canned food that produces a neurotoxin causing paralysis; toxin survives low-oxygen environments.

Clostridioides difficile (C.diff)

Causes long-term diarrhea after antibiotic treatment due to microbiome disruption (damage gut tissue from toxins).

Staphylococcus aureus —

Produces heat-stable enterotoxins in food that cause rapid food poisoning.

Salmonella enterica —

Invasive bacterium from undercooked eggs, meat, or dairy that causes food infection and diarrhea.

Rotavirus / Norovirus —

Viral causes of gastroenteritis with vomiting and watery diarrhea that spread rapidly.

Enterohemorrhagic E. coli (EHEC) —

Produces shiga toxin (block protein synthesis) causing bloody diarrhea and possible kidney failure.

Primary pathogen —

A pathogen that causes disease in healthy individuals.

Opportunistic pathogen —

A pathogen that only causes disease in immunocompromised hosts or when it enters protected body sites.

Ectoparasite —

A parasite that lives on the surface of a host.

Endoparasite —

A parasite that lives inside the body of a host.